Various methods exist for preparing difluoroacetic acid or salts thereof.
In particular, it is known practice to prepare difluoroacetic acid according to a chlorine-fluorine exchange reaction, by reacting potassium fluoride with dichloroacetic acid derivatives, for example N,N-diethylchlorofluoroacetamide (Chemical Abstracts 88, (1), 6300 m) or N-pyrrolidine-chlorofluoroacetamide (Chemical Abstracts 108, (19), 166949q).
An entirely different method for obtaining difluoroacetic acid lies in an oxidation reaction of difluoroethanol obtained by hydrolysis of 1-bromo-2,2-difluoroethane [Y. Désirant, Bull. Sci. Acad. Roy. Belg. [5] 15, 966-82 (1929)].
Another synthetic route is based on a dehydrohalogenation reaction starting with monochlorodifluoroacetic acid. Mention may be made in particular of U.S. Pat. No. 5,455,376, which describes the production of difluoroacetic acid via the gas-phase hydrogenation of monochlorodifluoroacetic acid, in the presence of a catalyst based on a noble metal, palladium or platinum, deposited on a support, for example alumina.
There is also a preparation process described in EP 1 137 615, via liquid-phase hydrogenation in a sodium hydroxide medium of monochlorodifluoroacetic acid, in the presence of Raney nickel. The chemical yield is good, but the production efficiency of such a process needs to be improved. There may be formation, as a side product, of monofluoroacetic acid, which is a particularly toxic product. Moreover, the acid obtained is in a sodium form, which is difficult to recover from the reaction medium.